Page 433 - Satellite Communications, Fourth Edition

Interference 413

13.4 Coordination
When a new satellite network is in the planning stage, certain calcula-
tions have to be made to ensure that the interference levels will remain
within acceptable limits. These calculations include determining the
interference that will be caused by the new system and interference it
will receive from other satellite networks.
In Sec. 13.2, procedures were outlined showing how interference may
be calculated by taking into account modulation parameters and carrier
frequencies of wanted and interfering systems. These calculations are very
complex, and the CCIR uses a simplified method to determine whether
coordination is necessary. As mentioned previously, where the potential for
interference exists, the telecommunication administrations are required
to coordinate the steps to be taken to reduce interference, a process referred
to as coordination.
To determine whether or not coordination is necessary, the interference
level is calculated assuming maximum spectrum density levels of the
interfering signals and converted to an equivalent increase in noise tem-
perature. The method is specified in detail in CCIR Report 454–3 (1982)
for a number of possible situations. To illustrate the method, one specific
situation where the existing and proposed systems operate on the same
uplink and downlink frequencies, will be explained here.
Figure 13.8a shows the two networks, R and Rr . The method will be
described for network Rr interfering with the operation of R. Satellite
Sr can interfere with the earth-station E, this being a B mode of inter-
1
ference, and earth-station Er can interfere with the satellite S,this
being a B mode. Note that the networks need not be physically adja-
2
cent to one another.

13.4.1 Interference levels
Consider first the interference B . This is illustrated in Fig. 13.8b. Let
1
U represent the maximum power density transmitted from satellite S′.
S
The units for U are W/Hz, or joules (J), and this quantity is explained
S
in more detail shortly. Let the transmit gain of satellite S′ in the direc-
tion of earth-station E be G′ , and let G be the receiving gain of earth-
E
S
station E in the direction of satellite S′. The interfering spectral power
density received by the earth station is therefore
[I ] [U ] [G′ ] [G ] [L ] (13.10)
S
E
D
S
1
where L is the propagation loss for the downlink. The gain and loss
D
factors are power ratios, and the brackets denote the corresponding
decibel values as before. The increase in equivalent noise temperature